1. Technical Field
This invention relates to printers for printing on media such as labels and, more particularly, to apparatus for holding a print face of a linerless media against the printing face of a printhead during printing without a platen member opposite the printing face, comprising, means for creating a reversed bend of the linerless media across the printing face and means for holding the reversed bend during printing by applying opposing forces to the linerless media across the printing face.
2. Background Art
There are numerous devices in the prior art which move and process strip media. As depicted in FIG. 1, it is a simple matter to dispose the media 10 between a driven roller 12 and a pinch roller 14 to move the media 10 as indicated by the arrow. Where the media 10 has no adhesive backing or where any adhesive is covered with a removable liner, the prior art approach of FIG. 1 can be used successfully.
In the field of tag and labels with particularity, there is a strong movement and demand for so-called "linerless" media. That is, the backing of the media is covered with an adhesive which is not covered with a removable liner during printing and process and up to the time of application to a surface. If media 10' having active adhesive 16 on its back surface is used in processing equipment configured as in FIG. 1, the result is as shown in FIG. 2. If the adhesive 16 is aggressive and has above minimal surface tenacity, it will strongly adhere to the roller 12 eventually causing the machinery to bind and come to a stop.
One approach in the industry has been to employ an adhesive which is only activated after processing. This can be done by heat, water, or some other means. This is fine if the application can employ the kind of adhesives which are post-processing activatable. Unfortunately, the pressure sensitive adhesives employed for tags and labels is not available in that form. If tags and labels are going to stay attached to packages and the like during the rigors of transit, a highly aggressive adhesive must be used. Such adhesives are only available in a form which remains active from application to the media.
It is very convenient to print on tags and labels using a thermal print head. Since printing is effected by heating each pixel position on the print surface that is to be a "dot" to the point that the thermal coating on the print surface changes color, it is important that there be a close thermal bond between the printhead elements providing the heat at each pixel position. To prevent bleeding from one pixel position to the other and allow rapid printing speeds, the heating and subsequent cooling of each element must be quick and very localized. Thus, in the prior art, it has been the standard approach to support the media to be printed upon within the print zone and opposite the printhead with a platen roller or platen surface. The printhead can then slide over the media in direct contact with the print surface. As can be appreciated from the drawing of FIG. 2, if one uses the prior art approach with linerless media, the platen roller or platen surface will quickly become fouled with adhesive and render the printer inoperable.
Wherefore, it is the object of this invention to provide methods and associated apparatus for printing on active adhesive linerless media without the use of a platen roller or platen surface with associated problems of binding, sticking, and the like.
Other objects and benefits of this invention will become apparent from the description which follows hereinafter when read in conjunction with the drawing figures which accompany it.